The present invention relates to a branched cyclodextrin or, more particularly, to a heterogeneous multiple-branched cyclodextrin (HEMB-CD) of which the branched portion of the molecular structure is composed of a combination of different saccharide moieties as well as to a method for the preparation of such HEMB-CD.
As is known, branched cyclodextrins have various excellent properties such as high solubility so that intensive investigations are under way on the method for the preparation and application development thereof. As a result of the hitherto undertaken investigations, several kinds of branched cyclodextrins have been reported including single-branched cyclodextrins in which the cyclodextrin ring has only one branched dextrin molecule bonded thereto such as .alpha.-1,4-glucans, e.g., glucose and maltose, panose and the like and HEMB-CD in which the cyclodextrin ring has two or more branches of the same saccharide molecules bonded thereto such as glucose, maltose and maltooligosaccharides, e.g., maltotriose. Exemplary of known heterogenous multiple-branched cyclodextrins are diglucosyl cyclodextrin of which a cyclodextrin ring has two glucosyl branches and dimaltosyl cyclodextrin of which a cyclodextrin ring has two maltosyl branches bonded thereto.
These heterogeneous multiple-branched cyclodextrins are prepared enzymatically from a branched cyclodextrin with an enzyme for cyclodextrin synthesis or from a mixture of a branched dextrin such as an .alpha.-1,4-glucan, e.g., maltose and maltotriose, panose and the like and a cyclodextrin and the reverse action of debranching enzyme.
Although single-branched cyclodextrins in general have a greatly increased solubility as compared to the starting cyclodextrin, some of the rings have only an insufficient effect on the increase of the solubility. Therefore, it is an important technical problem to develop various branched cyclodextrins having a branched structure of different saccharides bonded in different manners and to study the properties thereof.
Further, single-branched cyclodextrins such as single-branched .beta.-cyclodextrins are susceptible to the enzymatic activity of the starch-degrading enzyme, i.e. Takaamylase of Aspergillus oryzae so that it is increasingly demanded to develop a cyclodextrin compound highly resistant against the enzymatic activity of these enzymes.
As to the HEMB-CD, no heterogeneous multiple-branched cyclodextrin is known in the prior art of which a single cyclodextrin ring has two or more branches bonded thereto as derived from differnt kinds of saccharides such as glucose, maltose and the like. Much less, absolutely no information is available on the method for the preparation of such HEMB-CD.
It is a known art that the reverse reaction of a debranching enzyme such as pullulanase and the like can be utilized for the preparation of maltosyl cyclodextrins, maltotriosyl cyclodextrins, panosyl cyclodextrins, dimaltosyl cyclodextrins and the like from a combination of a cyclodextrin and maltose, maltotriose, panose and the like. Although this knowledge has been utilized to establish the method for the preparation of single-branched and heterogeneous multiple-branched cyclodextrins, it is not known that heterogeneous multiple-branched cyclodextrins are formed from a maltooligosaccharide and a glycosyl cyclodextrin by the reverse reaction of a debranching enzyme.